For increasingly complex electronic and computer devices, power source devices become increasingly important. Power source devices can be divided into two categories: linear type and switching type. Because linear-type power source devices have more disadvantages, all power source devices manufactured now all of the switching type.
The power supply for a backlight source of a TFT LCD panel makes use of an inverter circuit to convert DC power into AC power for energy conversion and driving of a cold cathode fluorescent lamp (CCFL). Conventional inverter circuits can be divided into push/pull-type, full-bridge-type and push/pull-type according to different circuit topologies. An inverter circuit is a circuit for converting DC power into AC power.
As shown in FIG. 1, a transformer T1 divides the circuit into a front-end circuit at the primary side 201 and a rear-end circuit at the secondary side 202. The front-end circuit at the primary side 201 comprises a DC voltage source Vcc, a first electronic switch Q1, and a second electronic switch Q2. The rear-end circuit at the secondary side 202 comprises a load. Reference is also made to FIG. 2. A first control signal a and a second control signal b are sent to control terminals A and B of the first and second electronic switches Q1 and Q2 to control switching actions of the first and second electronic switches Q1 and Q2 of the front end circuit 201, respectively. The actions of the first switch Q1 and the second switch Q2 are staggered by a small period of time, and are on/off alternately. The DC power source Vcc of the front-end circuit 201 is used to provide energy, and the transformer T1 raises and converts the voltage of the DC power Vcc to the rear-end circuit 202 for driving the load. The output voltage waveform c at the secondary side of the transformer T1 is the voltage waveform at point C. As shown in FIG. 2, the output voltage waveform c at the secondary side is an AC voltage waveform.
Reference is made to FIG. 1 again. The actions of the first switch Q1 and the second switch Q2 are slightly staggered by a small period of time, and are on/off alternately. Therefore, a small period of dead time is required for the control signals a and b shown in FIG. 2 to avoid burnout of the transformer T1 due to the first and second switches Q1 and Q2 being simultaneously on. Moreover, the control signals a and b need to control and change the switching actions of the first and second switches Q1 and Q2 for providing the required power for the load based on the power requirement of the load. Additionally, the control signals a and b need to stop the switching actions of the first and second switches Q1 and Q2 for accomplishing circuit protection according to various situations at the load end and various working statuses of the circuit, such as a too low output voltage, a too high output voltage, an open-circuited lamp or a too high temperature.